The present invention relates generally to the field of aircraft communications, and more particularly to a satellite based air traffic control system.
Air traffic control (ATC) systems rely on assembling and managing accurate information on aircraft location and course within specified zones and in communicating data, voice and other information to and from such aircraft. ATC systems must provide at least communications, navigation and surveillance functions. ATC systems control the airspace and airchannels between local airports, monitor the position and various flight control sensor information of aircraft within its region, provide voice and data communication between an air traffic controller and each aircraft within the airspace of its control for exchanging information such as route changes, weather and safety alerts, landing instructions, and information relating to crew or equipment emergency situations.
Present day ATC systems utilize an air traffic communication infrastructure that has been in place since the 1950s. In the U.S., this air traffic communication infrastructure includes more than 400 airport towers, 185 terminal radar approach control sites (Tracons), and 20 regional en route centers. Air traffic control, including navigation, surveillance and communication remains, for the most part, entirely ground based. Airport towers monitor the aircraft while it is on the ground. Flight plans and instructions for take-off and landing are communicated via AM radio. Tracon sites monitor the aircraft and give flight instructions during take-off, approach and landing. Tracon sites typically monitor the aircraft up to 40 miles out of an airport in lower altitudes. Regional en route centers take over control of the aircraft in high altitudes. Each regional en route center maintains control over aircraft flying within its region, which may cover areas between 20 and 200 miles wide. As an aircraft enters or leaves the region of control of a regional en route center, the regional en route center communicates with either the Tracon site or the regional en route center having control over the airspace from which the aircraft is entering or to which the aircraft is leaving to coordinate a hand-off of control of the aircraft. Tracon sites monitor aircraft within its airspace using airport surveillance radar (ASR), which typically has a range of approximately 55 nautical miles. Regional en route centers monitor aircraft within its airspace using air route surveillance radar, which typically has a range of approximately 200 nautical miles. A grid of very high-frequency omnidirectional range (VOR) transmitters across the United States provides navigational information for aircraft as they approach and pass over them.
Each country or group of countries typically has its own ATC system and navigational infrastructure. This increases the complexity and therefore the reliability of aircraft hand-offs between different ATC systems. Furthermore, each ATC system may provide coverage of the entire country or group of countries, but more typically covers only a large part of it. Thus, some areas of some countries, and some areas between countries such as ocean airspace and the airspace over the polar regions are uncovered. In uncovered areas, aircraft must be separated by much larger distances to maintain safe operation.
Present day ATC systems clearly suffer from many disadvantages. First, present day ATC systems cannot globally track all aircraft with uniform high precision without a substantial increase in the network of regional en route centers and ground radar installations. Setting up and maintaining these centers and radar installations is very costly. Furthermore, it is impractical in remote regions of the earth. Still further, ground radar installations may be more susceptible to sabotage in hostile areas.
Another disadvantage of the current ATC system is that quality of radar and radio communication signals transmitted via land line links is susceptible to atmospheric interference. Fog and rain result in backscatter which distorts the ground surveillance radar.
Yet another disadvantage of the current ATC system is that because ATC systems are fragmented worldwide, a given aircraft may not be under the control and surveillance of a single ATC system during the entire length of its flight.
Accordingly, a need exists for a single integrated system which provides global coverage of all of the communication, navigation and surveillance functions required by an ATC system.